The present invention relates to elastomeric compositions containing hydrophobicized silica. Elastomeric compositions of the invention are suitable, for example, for the manufacture of tires, tire tread, hose, industrial drive belts, conveyor belts and shoe soles.
In recent years, there has developed a considerable interest in silica reinforced tires, particularly since the appearance in 1992 of the Groupe Michelin (G-M) patents (EP 05 01 227 A 1; AU-A-111 77 192) indicating that tires made with tread formulations incorporating silica enjoy some important performance advantages over those based on conventional carbon black filler. Improvements are claimed for this xe2x80x9cGreen Tirexe2x80x9d in the areas of (a) lower rolling resistance, (b) better traction on snow and (c) lower noise generation, when compared with conventional tires filled with carbon black.
Rubber for tires is often supplied by a rubber producer to a tire manufacturer in the form of a masterbatch containing an elastomer, which is typically a hydrocarbon rubber, an oil extender and a filler. The traditional filler has been carbon black in the form of fine particles. These particles have hydrophobic surface characteristics and will therefore disperse easily within the hydrophobic elastomer. In contrast, silica has a very hydrophilic surface and considerable difficulty has been encountered in dispersing silica in the hydrophobic rubber elastomer.
In the past, efforts have been made to make masterbatches from elastomer dispersions and aqueous dispersions of silica pigment, such as those referred to and attempted by Burke, in U.S. Pat. No. 3,700,690. Burke attempted to overcome the previously known difficulties of incorporating fine particles of silica uniformly into a masterbatch. At the time of the Burke invention, there was no known elastomer-silica masterbatch offered in the commercial market. Similarly today, to the Applicant""s knowledge, there are no commercially available in situ produced elastomer-silica masterbatches in the market, despite the efforts of Burke (i.e., conventional elastomer-silica masterbatches are produced and available in the dry state).
It is an object of the present invention to obviate or mitigate at least one of the above-mentioned disadvantages of the prior art.
It is another object of the present invention to provide a novel masterbatch composition.
Thus, in one of its aspects, the present invention provides a rubber masterbatch composition comprising a solution SBR (styrene-butadiene rubber) and silica particles.
In one embodiment, the solution SBR may be a low vinyl, low styrene solution SBR. In another embodiment, the solution SSR may comprise a mixture of a solution SBR (i.e., virtually any solution SBR) and solution BR (butadiene rubber).
In another of its aspects, the present invention provides an elastomeric composition which comprises:
(i) a solution SBR/silica-containing masterbatch, which contains preferably from about 40 to about 120 parts by weight of silica per 100 parts by weight of polymer, and
(ii) a solution BR/silica-containing masterbatch, which contains preferably from about 40 to about 120 parts by weight of silica per 100 parts by weight of polymer;
wherein the silica has been hydrophobicized.
The present compositions may be characterized, inter alia, by being useful in the production of vulcanizates have an improvement in one or more of the following properties: traction, abrasion and rolling resistance.
As used throughout this specification, the term xe2x80x9csolution SBRxe2x80x9d is intended to mean a styrene-butadiene rubber produced by a process in which polymerization of the styrene and butadiene monomers is catalyzed in the presence of a solvent (typically a hydrocarbon solvent). The solution SBR typically has a glass transition temperature (Tg) of between 0xc2x0 C. and xe2x88x9280xc2x0 C., when measured by differential scanning calorimeter.
As disclosed hereinabove, in one embodiment of the present invention, the solution SBR may be a single elastomer in the form of a low-vinyl, low styrene solution SBR. The term xe2x80x9clow vinyl, low styrene solution SBRxe2x80x9d, as used throughout this specification, is meant to encompass a solution SBR having a vinyl content of less than about 40% (preferably in the range of from about 5 to about 40%, more preferably in the range of from about 5 to about 30%, most preferably in the range of from about 5 to about 25%) and a styrene content in the range of from about 5 to about 25% (preferably in the range of from about 10 to about 25%, most preferably in the range of from about 15 to about 25%). In this embodiment, the composition comprises a masterbatch of the low vinyl, low styrene solution SBR and the silica particles.
As further disclosed hereinabove, in another embodiment of the present invention, the solution SBR may comprise a mixture of a solution SBR and a solution BR. In a first version of this embodiment, the composition comprises a mixture of a first masterbatch comprising solution SBR/silica particles and a second masterbatch comprising solution BR/silica particles. In a second version of this embodiment, the composition comprises a single masterbatch derived from a mixture of polymer cementsxe2x80x94i.e., a mixture of solution SBR and solution BR cements is first made and then contacted with the silica particles to produce the masterbatch.
The solution SBR may be suitably prepared in solution and may have a styrene content in the range of from about 15 to about 25% by weight and a glass transition temperature (Tg) of between 0xc2x0 C. and xe2x88x9280xc2x0 C., when measured by differential scanning calorimeter. The content of vinyl bonds in the butadiene fraction incorporated can be in the range of from about 30 to about 75%, preferably in the range of from about 50 to about 75%. The content of trans-1,4 bonds can be between 15 and 60%, and the content of cis 1,4 bonds is complementary to the content of vinyl bonds plus trans-1,4 bonds. The vinyl bonds content of the copolymer is preferably greater than 50%. Particularly preferred is Buna VSL 5025-1 (formerly Buna VSL 1950S25, commercially available from Bayer Inc.) which is a co-polymer of styrene and butadiene, the styrene content being about 25% and the vinyl content in the butadiene portion being about 67%.
As used throughout this specification, the term xe2x80x9csolution BRxe2x80x9d is intended to mean a butadiene rubber produced by a process in which polymerization of the butadiene monomer is catalyzed in the presence of a solvent (typically a hydrocarbon solvent). Preferably, the solution BR is a high cis polybutadiene, more preferably a solution BR having more than 90% cis-1,4 bonds. The production of such a solution BR can be achieved by known methods of catalysis with the use of transition metals as described, for instance in French Patent No. 143 6607. A particularly preferred solution BR is Taktene 1203 (available from Bayer), which has a cis content of about 96%.
The composition preferably contains from about 30 to about 100 parts per 100 parts of total polymer (phr) of silica. Preferably it also contains from about 25 to about 50 parts per 100 parts of total polymer (phr) of aromatic oil, selected from those known in rubber processing.
As stated above, the silica particles are hydrophobicized. A preferred method for hydrophobicizing silica particles is described in copending International patent application PCT/CA98/00499, the contents of which are hereby incorporated by reference. This preferred process comprises the steps of:
(a) contacting the particles with a compound of Formula I: 
xe2x80x83or an acid addition or quaternary ammonium salt thereof, in which:
at least one of R1, R2 and R3, preferably two of R1, R2 and R3 and most preferably R1, R2 and R3 are hydroxyl or hydrolysable groups;
R4 is a divalent group that is resistant to hydrolysis at the Sixe2x80x94R4 bond;
R5 is selected from the group comprising: hydrogen; a C1-40 alkyl; a C2-40 mono-, di- or tri-unsaturated alkenyl group; a C6-C40 aryl group; a group of the formula: 
xe2x80x83in which x is an integer from 2 to 10, R13 and R14, which may be the same or different, are each hydrogen; C1-18 alky; C2-18 , mono-, di- or tri-unsaturated alkenyl; phenyl; a group of formula: 
xe2x80x83wherein b is an integer from 1 to 10; a group of formula: 
xe2x80x83wherein c is an integer from 1 to 10 and R22 and R23 which may be the same or different, are each hydrogen, C1-10 alkyl group or C2-10 alkenyl group, provided that there is no double bond in the position alpha to the nitrogen atom; a group of formula:
xe2x80x94[(CH2)rNH]dxe2x80x94H
xe2x80x83wherein r is an integer from 1 to 6 and d is an integer from 1 to 4;
R6 may be any of the groups defined for R5, or R5 and R6 may together form a divalent group of formula: 
xe2x80x83in which A is selected from the group comprising xe2x80x94CHR or xe2x80x94NR group in which R is hydrogen or a C1-40 alkyl or C2-40 alkeny. group, a C6-C40 aryl group, an oxygen atom and a sulfur atom, and t and v are each independently 1, 2, 3 or 4; provided that the sum of t and v does not exceed 6, and is preferably 4; and
(b) contacting the particles with a compound of the Formula II: 
xe2x80x83in which:
R15, R16 and R17 have the same definitions as R1, R2 and R3; and
R12 is selected from the group comprising a C8-40 alkyl group or a C8-40 mono-, di- or tri-unsaturated alkenyl group, either of which can be interrupted by one or more aryl groups, preferably phenyl groups; a group of formula: 
xe2x80x83or an acid addition or quaternary ammonium salt thereof in which R18 is a divalent group resistant to hydrolysis at the Sixe2x80x94R18 bond, R19 is selected from the group comprising hydrogen, a C1-40 alkyl group, a C2-40 mono-, di- or tri-unsaturated alkenyl group, a substituted aromatic group, for example the phenylene group xe2x80x94(C6H4)xe2x80x94, the biphenylene group xe2x80x94(C6H4)xe2x80x94(C6H4)xe2x80x94, the xe2x80x94(C6H4)xe2x80x94Oxe2x80x94(C6H4)xe2x80x94 group or the naphthylene group, xe2x80x94(C10H6)xe2x80x94, the aromatic group being unsubstitued or substituted by a C1-20 alkyl or C2-20 mono-, di- or tri-unsaturated alkenyl group; and R20 may be any of the groups defined for R19, with the provisos that R19 and R20 do not have a tertiary carbon atom adjacent to the nitrogen atom and that at least one of R19 and R20 has a carbon chain at least 8 carbon atoms in length uninterrupted by any heteroatoms.
Preferably, R18 is a C1-C40 saturated or unsaturated group (e.g., alkenyl, aryl, cycloalkyl and the like).
In the process, Steps (a) and (b) may be conducted concurrently or sequentially. If Steps (a) and (b) are conducted sequentially, it is preferred to conduct Step (a) followed by Step (b).
As will be apparent to those of skill in the art, there are instances where Formulae I and II may be the same compoundxe2x80x94e.g., when R5xe2x95x90R19xe2x95x90 a C8-40 alkyl group or R5xe2x95x90R19xe2x95x90 a C8-40 mono-, di- or tri-unsaturated alkenyl group. Thus, in such cases where Formulae I and II are the same compound, it will be clearly understood that the process intentionally embodies a single step process (i.e., where the compound of Formulae I and II is added in a single step) and a multi-step process (i.e., where the compound of Formulae I and II is added proportionally in two or more steps).
Preferably, the process is carried out in an aqueous solution, dispersion or slurry, so that the product of the process is an aqueous dispersion or slurry of hydrophobicized mineral particles.
In one preferred embodiment, the dispersion or slurry resulting from the process, and containing the treated particles (preferably mineral particles such as silica), is then mixed with a hydrocarbon solution of the elastomer (i.e., low vinyl, low styrene solution SBR, solution SBR or solution BR), and then dried to form a silica-filled rubber masterbatch. Owing to the hydrophobicized nature of the silica filler, it is well dispersed in the elastomer. This preferred embodiment results in the in situ production of a masterbatch composition comprising the elastomer and the treated particles. By xe2x80x9cin situ productionxe2x80x9d is meant that treated particles are incorporated into a masterbatch composition without being isolated (i.e., separated from the dispersion or slurry, and subsequently dried). This preferred embodiment is believed to be the first in situ production of a masterbatch composition comprising solution SBR and a treated particulate material such as silica.
In a preferred embodiment, the treatment is carried out in an aqueous dispersion or slurry and the concentration of the aqueous dispersion or slurry of silica particles may be between 1 and 30 percent by weight of silica in water, preferably between 5 and 25 percent by weight of silica in water and most preferably between 8 and 22 percent by weight of silica in water. Dried amorphous silica suitable for use in accordance with the invention may have a mean agglomerate particle size between 1 and 100 microns, preferably between 10 and 50 microns and most preferably between 10 and 25 microns. It is preferred that less than 10 percent by volume of the agglomerate particles are below 5 microns or over 50 microns in size. A suitable amorphous dried silica moreover has a BET surface area, measured in accordance with DIN (Deutsche Industrie Norm) 66131, of between 50 and 450 square meters per gram and a DBP absorption, as measured in accordance with DIN 53601, of between 150 and 400 grams per 100 grams of silica, and a drying loss, as measured according to DIN ISO 787/II, of from 0 to 10 percent by weight. If filter cake is used, it may be made by any known means such as described in Ullmann""s Encyclopedia of Industrial Chemical Vol A23 pages 642-643, VCH Publishers, (copyright)1993. The filter cake has a preferred solids content of between 5 and 30 percent by weight, most preferably between 15 and 25 percent by weight, and it may be redispersed in water in accordance with the process to give a silica concentration of between 5 and 20 percent by weight and most preferably between 8 and 12 percent by weight. It is preferred to use a filter cake.
If a never-filtered slurry prepared from the known reaction of a solution of alkali metal silicate with either mineral acid or carbon dioxide is used, it is preferred that the solids content of the never-filtered slurry be between 1 and 30, more preferably between 5 and 10, percent by weight of silica. The slurry temperature may be between 0 and 100 degrees Celsius if the process is conducted at atmospheric pressure or between 0 and 135 degrees Celsius if the operation is conducted in a pressure vessel. Most preferably, the process is conducted at atmospheric pressure in which case the preferred temperature is between 30 and 95 degrees Celsius and most preferably between 45 and 90 degrees Celsius.
It is desirable that, prior to the addition to the silica particles of the compound of Formula I, the dispersion or slurry shall have a pH in the range from 6 to about 8, more preferably from about 6.8 to about 7.2. If necessary, the pH can be adjusted by addition of acid or alkali, for example mineral acid, alkali metal hydroxide, alkaline earth hydroxide, ammonium hydroxide and the like. These can be added as such or in aqueous solution.
In the compound of Formula I, it is preferred that all three of the groups R1, R2 and R3 are readily hydrolysable. Suitable groups R1 include hydroxyl groups and hydrolysable groups of formula OCpH2p+1 where p has a value from 1 to 10. The alkyl chain can be interrupted by oxygen atoms, to give groups, for example, of formula CH3OCH2Oxe2x80x94, CH3OCH2OCH2Oxe2x80x94, CH3(OCH2)4Oxe2x80x94, CH3OCH2CH2Oxe2x80x94, C2H5OCH2Oxe2x80x94, C2H5OCH2OCH2Oxe2x80x94, or C2H5OCH2CH2Oxe2x80x94. Other suitable hydrolysable groups include phenoxy, acetoxy, chloro, bromo, iodo, ONa, OLi, OK or amino or mono- or dialkylamino, wherein the alkyl group(s) have 1 to 30 carbon atoms.
R2 and R3 can take the same values as R1, provided that only one of R1, R2 and R3 is chloro, bromo or iodo. Preferably, only one or two of R1, R2 and R3 is hydroxyl or ONa, OLi or OK.
Non-limiting examples of groups R2 and R3 that are not hydrolysable include C1-10 alkyl, C2-10 mono- or diunsaturated alkenyl, and phenyl. R2 and R3 can also each be a group xe2x80x94R4xe2x80x94NR5R6, discussed further below. It is preferred that R1, R2 and R3 are all the same and are CH3Oxe2x80x94, C2H5Oxe2x80x94 or C3H8Oxe2x80x94. Most preferably they are all CH3Oxe2x80x94.
The divalent group R4 is preferably such that Nxe2x80x94R4xe2x80x94Si is of the formula:
Nxe2x80x94(CH2)p(O)o(C6H4)n(CH2)m(CHxe2x95x90CH)kxe2x80x94Si
in which k, m, n, o and p are all whole numbers. The order of the moieties between N and Si is not particularly restricted other than neither N or O should be directly bound to Si. The value of k is 0 or 1, the value of m is from 0 to 20 inclusive, the value of n is 0, 1 or 2, the value of o is 0 or 1 and the value of p is from 0 to 20 inclusive, with the provisos that the sum of the values of k, m, n, o and p is at least 1 and not more than 20 and that if o is 1, p is 1 or greater and the sum of k, m and n is 1 or greater, i.e. that the Si atom is linked directly to a carbon atom. There should be no hydrolysable bond between the silicon and nitrogen atoms. Preferably, m is 3 and l, n, o and p are all 0, i.e., R4 is xe2x80x94CH2CH2CH2xe2x80x94.
The group R5 is preferably a C8-20 monounsaturated alkenyl group, most preferably a C16-18 monounsaturated alkenyl group. R6 is preferably hydrogen.
Suitable compounds of Formula I include, but are not limited to: 3-aminopropylmethyldiethoxysilane, N-2-(vinylbenzylamino)-ethyl-3-aminopropyl-trimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxy-silane, trimethoxysilylpropyldiethylenetriamine, N-2-(aminoethyl)-3-aminopropyltris(2-ethylhexoxy)silane, 3-aminopropyldiisopropylethoxysilane, N-(6-aminohexyl)aminopropyltrimethoxysilane, 4-aminobutyltriethoxysilane, 4-aminobutyldimethylmethoxysilane, triethoxysilylpropyl-diethylenetriamine, 3-aminopropyltris(methoxyethoxyethoxy)silane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltris(2-ethylhexoxy)silane, 3-aminopropyldiisopropylethoxysilane, N-(6-aminohexyl)aminopropyltrimethoxysilane, 4-aminobutyltriethoxysilane, and (cyclohexylaminomethyl)-methyidiethoxysilane.
Preferred compounds of Formula I include those in which R5 is hydrogen and R6 is the alkenyl group from the following: soya alkyl, tall oil alkyl, stearyl, tallow alkyl, dihydrogenated tallow alkyl, cocoalkyl, rosin alkyl, and palmityl, it being understood that in this case the alkyl may include unsaturation.
It is preferred that at least one of R4, R13 and R14 has a chain of at least 8 carbon atoms, more preferably at least 10 carbon atoms, uninterrupted by any heteroatom.
The compound of Formula I can be used as the free base, or in the form of its acid addition or quaternary ammonium salt, i.e. 
wherein R1, R2, R3, R4, R5 and R6 are as defined above; R7 is selected from the group comprising hydrogen, a C1-40 alkyl group or C2-40 mono-, di- or tri-unsaturated alkenyl group, and X is an anion. X is suitably chlorine, bromine, or sulphate, of which chlorine and bromine are preferred, and R7 is preferably hydrogen.
Non-limiting examples of suitable salts of compounds of Formula I include N-oleyl-N-[(3-triethoxysilyl)propyl]ammonium chloride, N-3-aminopropylmethyidiethoxy-silane hydrobromide, (aminoethylaminomethyl)phenyltrimethoxysilane hydrochloride, N-[(3-trimethoxysilyl)propyl]-N-methyl, N-N-diallylammonium chloride, N-tetradecyl-N,N-dimethyl-N-[(3-trimethoxysilyl)propyl]ammonium bromide, 3[2-N-benzylaminoethylaminopropyl]trimethoxysilane hydrochloride, N-octadecyl-N,N-dimethyl-N-[(3-tri-methoxysilyl)propyl]ammonium bromide, N-[(trimethoxysilyl)propyl]-N-tri(n-butyl)ammonium chloride, N-octadecyl-N-[3-triethoxysilyl)propyl]ammonium chloride and N-2-(vinylbenzylamino)ethyl-3-aminopropyl-trimethoxysilane hydrochloride.
It is preferred to use the compound of Formula I in salt form. The most preferred compound is N-oleyl-N-[(3-trimethoxysilyl)propyl]ammonium chloride.
The amount of the compound of Formula I may be between 0.1 and 20 percent by weight of the mineral particles in the slurry (dry basis) and preferably between 0.25 and 10 percent by weight and most preferably between 0.5 and 2 percent by weight. Preferably, the amount of the compound of Formula I used varies inversely with the mineral particle size. The compound may be added to the slurry in its natural state, either as a liquid or a solid. However, to facilitate dispersion, it is preferred where possible to add the compound as a liquid. If the melting point of the compound is below 95 degrees Celsius, it is preferred to add it to the slurry in a molten state at a temperature at least 5 degrees Celsius above the melting point, provided the temperature of the compound in the liquified state does not exceed 100 degrees Celsius and provided that the compound does not decompose under these conditions. If the melting point exceeds 95 degrees Celsius, it is most preferred to use a solvent. Preferred solvents are water and alcohols containing 1 to 5 carbon atoms and most preferably those containing 1 to 3 carbon atoms, that is to say methanol, ethanol, n-propanol or isopropanol. If the compound of Formula I is an alkoxysilane, then most preferably the alkoxy group of the solvent alcohol will be the same as the alkoxy group of the alkoxysilane. For example, if the compound of Formula I is a methoxysilane, the preferred solvent is methanol. The concentration of the compound in the solvent may be from 10 to 90 percent by weight and more preferably between 25 and 75 percent by weight and most preferably 50 percent by weight. Preferably, the solution can be prepared and added to the slurry at a temperature between a lower limit of 0 degrees Celsius and an upper limit which is the lower of at least 10 degrees below the boiling point of the solvent and 95 degrees Celsius. The dispersion of the compound is effected by mixing.
It is preferred that, for the specific compound of Formula I which is added, the equivalent balance (EB) should be calculated. The EB is used to determine whether mineral acid or alkali metal hydroxide, or solution thereof, should be added. The equivalent balance (EB) may be determined from the absolute value of the sum of the group values of X (if present), R1, R2 and R3 and the magnitude of the sum of the group contributions of X (if present), R1, R2 and R3 together with the weight added and the molecular weight of the compound of Formula I, according to the following scheme: The group contribution of X for either X=CI or X=Br is xe2x88x921, thus, if X is present, it is given a value of xe2x88x921. The group contribution of each of R1, R2 and R3 is generally zero for all groups except as follows: if the group is CH3COO, Cl or Br, in which case it is xe2x88x921, or if it is amine (including an imine), ONa, OK or OLi in which case it is +1. If the sum of the group contributions for X, R1, R2 and R3 is zero, no adjustment with mineral acid or alkali metal hydroxide (or solutions thereof) is necessary. If the sum of the group values is a positive integer, adjustment with mineral acid is desirable, and if it is negative, adjustment with alkali metal hydroxide is desirable.
For example, where R1=OCH3, R2=CH3, R3=Cl and X=Br, the sum of the group values (g.v.) is:
xcexa3=(g.v. OCH3)+(g.v. CH3)+(g.v. Cl)+(g.v. Br)=(0)+(0)+(xe2x88x921)+(xe2x88x921)=xe2x88x922
The negative sign in front of the sum indicates adjustment with alkali metal hydroxide is required. The number of equivalents of alkali required is given by the equivalent balance (EB) which includes the absolute value of the sum of the group contributions (|xcexa3|) as a scaling factor:   EB  =                    "LeftBracketingBar"        Σ        "RightBracketingBar"            xc3x97      weight      ⁢              xe2x80x83            ⁢      in      ⁢              xe2x80x83            ⁢      grams      ⁢              xe2x80x83            ⁢      of      ⁢              xe2x80x83            ⁢      the      ⁢              xe2x80x83            ⁢      chemical      ⁢              xe2x80x83            ⁢      added              molecular      ⁢              xe2x80x83            ⁢      weight      ⁢              xe2x80x83            ⁢      of      ⁢              xe2x80x83            ⁢      the      ⁢              xe2x80x83            ⁢      added      ⁢              xe2x80x83            ⁢      chemical      
In continuing the example, if a process according to the present invention were scaled so as to require 6,000 grams of a chemical of Formula I with a molecular weight of 350 grams and the sum of the group values gave xe2x88x922, EB would be calculated as follows:
EB=xe2x88x922xc3x976000/350=xe2x88x9234.28 gram-equivalents
Thus, in this example, 34.28 gram-equivalents of alkali metal hydroxide would be added. Sodium hydroxide is the preferred alkali metal hydroxide. The weight of sodium hydroxide would be:
Weight=(EB)xc3x97(Equivalent Weight of NaOH)=34.28xc3x9740.0=1371.2 grams
The preferred technique according to the invention is to dissolve the alkali metal hydroxide or mineral acid in water so as to obtain a concentration between 5 and 25% by weight and most preferably between 5 and 10% by weight prior to adding the solution to the slurry.
It is known to incorporate a coupling agent into rubber that is intended to be vulcanized and used, for instance, in tires. Suitable coupling agents include those described in U.S. Pat. No. 4,704,414, published European patent application 0,670,347A1 and published German patent application 4435311A1, the disclosures of each of which are incorporated by reference. One suitable coupling agent is a mixture of bis[3-(triethoxysilyl)propyl]monosulfane, bis[3-(triethoxysilyl)propyl]disulfane, bis[3-(triethoxysilyl)propyl]trisulfane and bis[3-(triethoxysilyl)propyl]tetrasulfane and higher sulfane homologuesxe2x80x94for example, coupling agents available under the trade names Si-69 (average sulfane 3.5), Silquest(trademark) A-1 589 or Si-75 (average sulfane 2.0). Another non-limiting examples of a suitable coupling agent is bis[2-(triethoxysilyl)ethyl]tetrasulfane, available under the trade name Silquest RC-2. In the past, achieving a good balance between the coupling agent and particles, such as silica, without scorching or premature curing has proven difficult. In accordance with the invention, if particles, particularly silica particles, are being treated to render them hydrophobic for use in rubber which is subsequently to be vulcanized, it is possible to include a step of adding a coupling agent in the process of the invention, so that the coupling agent becomes attached to the surface of the hydrophobicized mineral particles and becomes dispersed in the rubber with the mineral particles.
Thus, in some preferred embodiments of the invention, a coupling agent is added to the dispersion, more preferably after the addition of the compound of Formula I but before the compound of Formula II is added. As discussed above, in some cases, Formulae I and II may represent the same compound. In these cases, it is preferred to add the coupling agent between sequential additions of the compound of Formulae I and II.
The coupling agent may be added after any addition of mineral acid or alkali metal hydroxide that is indicated by the calculation of the EB. Non-limiting examples of suitable coupling agents include compounds of formula:
R8R9R10MR11
in which at least one of R8, R9 and R10, preferably two of R8, R9 and R10 and most preferably R8, R9 and R10, are hydroxyl or hydrolysable groups. The groups R8, R9 and R10 are bound to the atom M, which is silicon, titanium or zirconium. The group R8 may be hydroxyl or OCpH2p+1 where p is from 1 to 10 and the carbon chain may be interrupted by oxygen atoms, to give groups, for example, of formula CH3OCH2Oxe2x80x94, CH3OCH2OCH2Oxe2x80x94, CH3(OCH2)4Oxe2x80x94, CH3OCH2CH2Oxe2x80x94, C2H5OCH2Oxe2x80x94, C2H5OCH2OCH2Oxe2x80x94 or C2H5OCH2Oxe2x80x94. Alternatively R8 may be phenoxy. If M is titanium or zirconium, R8 may be the neopentyl(diallyl)oxy group, but not if M is silicon. The group R9 may be the same as R8. If M is silicon, R9 may also be a C1-10 alkyl group, a phenyl group, or a C2-10 mono- or diunsaturated alkenyl group. If M is titanium or zirconium, R9 may be the neopentyl(diallyl)oxy group, but not if M is silicon. Further, R9 may be the same as the group R11 described below.
R10 may be the same as R8, but it is preferred that R8, R9 and R10 are not all hydroxyl. If M is silicon, R10 may also be C1-10 alkyl, phenyl, C2-10 mono- or diunsaturated alkenyl. If M is titanium or zirconium, R10 may be the neopentyl(diallyl)oxy group, but not if M is silicon. Further R10 may be the same as the group R11 described below.
The group R11 attached to M is such that it may participate in a crosslinking reaction with unsaturated polymers by contributing to the formation of crosslinks or by otherwise participating in crosslinking. In the case where M is silicon, R11 may have one of the following structures: R11 may represent the allyl group xe2x80x94H2CCHxe2x95x90CH2, the vinyl group xe2x80x94CHxe2x95x90CH2, the 5-bicycloheptenyl group or the group described by
xe2x80x94(alk)e(Ar)fSi(alk)g(Ar)hSiR8R9R10
where R8, R9 and R10 are the same as previously defined, alk is a divalent straight hydrocarbon group having between 1 and 6 carbon atoms or a branched hydrocarbon group having between 2 and 6 carbon atoms, Ar is either a phenylene xe2x80x94C6H4xe2x80x94, biphenylene xe2x80x94C6H4xe2x80x94C6H4xe2x80x94 or xe2x80x94C6H4xe2x80x94OC6H4xe2x80x94 group and e, f, g and h are either 0, 1 or 2 and i is an integer from 2 to 8 inclusive with the provisos that the sum of e and f is always 1 or greater than 1 and that the sum of g and h is also always 1 or greater than 1. Alternately, R11 may be represented by the structures (alk)e(Ar)fSH or (alk)e(Ar)fSCN where e and f are as defined previously. Moreover, it is possible for R11 to have the structure
xe2x80x94(CHxe2x95x90CH)k(CH2)m(C6H4)n(O)o(CH2)pR13
wherein k, m, n and o and p are all whole numbers and R13 represents the acryloxy CH2xe2x95x90CHCOOxe2x80x94 or the methacryloxy CH2xe2x95x90CCH3COOxe2x80x94 group. Further, the value of k may be 0 or 1, m may be from 0 to 20 inclusive, n may be between 0 and 2, o may be 0 or 1, and p may be from 0 to 20 inclusive, with the provisos that the sum of k, m, n and o is at least 1 and not greater than 20, and that if n is 1 or 2 or o is 1, p is 1 or greater. It is most preferable that m=3 and k, n, o and p are all 0.
Preferably, R8, R9 and R10 are all either OCH3, OC2H5 or OCH8 groups and most preferably all are OCH3 groups. It is most preferred that the coupling agent is bis[3-(trimethoxysilyl)propyl]tetrasulfane (Si-168). The amount of coupling agent to add is optional; levels between 2 and 10 percent by weight of the silica in the slurry (dry basis) are preferred. The dispersion of the chemical may be effected by mixing.
Non-limiting illustrative examples of other coupling agents, include the following: bis[(trimethoxysilyl)propyl)]disulfane (Si-166), bis[(triethoxysilyl)propyl)]disulfane (Si-266), bis[2-(trimethoxysilyl)ethyl]-tetrasulfane, bis[2-(triethoxysilyl)ethyl]trisulfane, bis[3-(trimethoxysilyl)propyl]-disulfane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 3-mercaptoethylpropylethoxymethoxysilane, 1,3-bis(3-acryloxypropyl)tetramethoxydisiloxane, acryloxypropylmethyldimethoxysilane, 3-methacryloxypropyl-trimethoxysilane, allyltrimethoxysilane, diallyldiethoxysilane, 5-(bicycloheptenyl)triethoxysilane, 5-(bicycloheptenyl)methylmethoxyethoxysilane, isopropoxytriacryltitanate, diisopropyldimethacryltitanate, diethoxydi(3-mercaptopropoxy)zirconate, triisopropoxy-(2-mercaptoethoxy)zirconate, and di[neopentyl(diallyl)oxy]-di(3-mercaptopropoxy)-zirconate.
Other preferred coupling agents include those disclosed in published German patent application 44 35 311 A1. On pages 2 and 3, there is disclosure of oligomers and polymers of sulphur containing organooxysilanes of the general formula: 
in which R1 is a saturated or unsaturated, branched or unbranched, substituted or unsubstituted hydrocarbon group that is at least trivalent and has from 2 to 20 carbon atoms, provided that there are at least two carbon-sulphur bonds, R2 and R3, independently of each other, are saturated or unsaturated, branched or unbranched, substituted or unsubstituted hydrocarbon groups with 1 to 20 carbon atoms, halogen, hydroxy or hydrogen, n is 1 to 3, m is 1 to 1000, p is 1 to 5, q is 1 to 3 and x is 1 to 8.
Preferred compounds are of the general formula 
wherein R2, m and x have the meanings given above, and R2 is preferably methyl or ethyl. These compounds disclosed in German Patent Application No. 44 35 311 A1 are preferred coupling agents for use in the present invention.
Also preferred for use in this invention are coupling agents disclosed in the abbvementioned published European patent application 0,670,347A1, which discloses coupling agents of the general formula:
R1R2R3Sixe2x80x94X1xe2x80x94(xe2x80x94Sxxe2x80x94Yxe2x80x94)mxe2x80x94(xe2x80x94Sxxe2x80x94X2xe2x80x94SiR1R2R3)n
in which R1, R2 and R3 are the same or different and are C1-8 alkyl, C1-8 alkoxy, phenyl or phenoxy, provided that at least one of R1, R2 and R3 is an alkoxy or phenoxy group. X1 and X2 are the same or different and are divalent linear or branched, optionally unsaturated C1-12 alkyl groups, Y is a di-, tri- or tetravalent linear, branched or cyclic C1-18 alkyl group that is optionally unsaturated and is optionally substituted by C6-12 aryl, C1-8 alkoxy or hydroxy groups and which can be interrupted by oxygen, sulphur or nitrogen atoms or aromatic C6-12 aryl groups, or Y is a C6-12 aryl or heteroaryl group, m is an integer from 1 to 20, n is an integer from 1 to 6 and x is an integer from 1 to 6.
Particularly preferred coupling agents are those of the following general formulae:
(RO)3SiCH2CH2CH2"Brketopenst"Sxxe2x80x94CH2CH2"Brketclosest"nSxxe2x80x94CH2CH2CH2Si(OR)3
in which R=xe2x80x94CH3 or xe2x80x94C2H5, x=1-6 and n=1-10; 
in which R=xe2x80x94CH3 or xe2x80x94C2H5, x=1-6 and n=1-10;
(RO)3SiCH2CH2CH2"Brketopenst"Sxxe2x80x94CH2)6"Brketclosest"nSxxe2x80x94CH2CH2CH2Si(OR)3
in which R=xe2x80x94CH3, xe2x80x94C2H5 or xe2x80x94C3H7, n=1-10 and x=1-6; 
in which R=xe2x80x94CH3, xe2x80x94C2H5 or xe2x80x94C3H7, n=1-10 and x=1-6; 
in which R=xe2x80x94CH3, xe2x80x94C2H5 or xe2x80x94C3H7, n=1-10 and x=1-6;
(RO)3Sixe2x80x94CH2CH2CH2"Brketopenst"Sxxe2x80x94CH2CH2OCH2CH2"Brketclosest"nSxxe2x80x94CH2CH2CH2Si(OR)3
in which R=xe2x80x94CH3, xe2x80x94C2H5, xe2x80x94C3H7, n=1-10 and x=1-6; 
in which R=xe2x80x94CH3, xe2x80x94C2H5 or C3H7, n 1-10 and x=1-6; 
in which R=xe2x80x94CH3, xe2x80x94C2H5, or xe2x80x94C3H7; R1=xe2x80x94CH3, xe2x80x94C2H5, xe2x80x94C3H7, xe2x80x94C6H5, xe2x80x94OCH3, xe2x80x94OC2H5, xe2x80x94OC3H7 or xe2x80x94OC6H5, n=1-10 and x=1-8; and
(RO)3Sixe2x80x94CH2CH2CH2"Brketopenst"Sxxe2x80x94(CH2)6"Brketclosest"r"Brketopenst"Sxxe2x80x94(CH2)8"Brketclosest"pCH2CH2CH2Si(OR3)
in which R=xe2x80x94CH3, xe2x80x94C2H5 or xe2x80x94C3H7, r+p=2-10 and x=1-6.
Especially preferred are coupling agents of the formulae:
(RO)3SiCH2CH2CH2"Brketopenst"Sxxe2x80x94(CH2CH2)6"Brketclosest"nSxxe2x80x94CH2CH2CH2xe2x80x94Si(OR)3

in which x is 1-6 and n is 1-4.
In Step (b) of the process, the compound of Formula II is added to the particulate filler material. Again, it is preferred that the particulate filler material, more preferably a mineral filler, is in the form of an aqueous slurry or a dispersion, and the compound of Formula II is added to the slurry or dispersion under intense mixing. In the compound of Formula II the possible and preferred values for R15, R16 and R17 are the same as the possible and preferred values for R1, R2 and R3 that are discussed above in relation to Formula I. If R12 is an amino group of formula xe2x80x94R18xe2x80x94NR19R20, preferred values for R18 are such that Nxe2x80x94R18xe2x80x94Si includes groups of the formula:
Nxe2x80x94(CH2)p(O)o(C6H4)n(CH2)m(CHxe2x95x90CH)kxe2x80x94Si
in which k is 0 or 1, m is 0 to 20 inclusive, n is 0, 1 or 2, o is 0 or 1 and p is 0 to 20 inclusive, provided that the sum of k, m, n, o and p is at least 1 and not greater than 20, and further provided that if o is 1, p is also 1 or greater, and the sum of k, m and n is 1 or greater. The order of the moieties between N and Si is not particularly restricted other than neither N or O should be directly bound to Si. There should be no hydrolysable group between the silicon and nitrogen atoms. Preferably k, n, o and p are all 0 and m is 3, i.e. R18 is xe2x80x94CH2CH2CH2xe2x80x94.
R12 may be a moiety containing at least one primary, secondary, or tertiary amine nitrogen. In this case the amino group bonded to R18xe2x80x94 is given by the formula xe2x80x94NR19R20. R19 may be a H or a C1-40 alkyl group or a C2-40 mono-, di- or tri-unsaturated alkenyl group. R19 may also be a C1-20 alkyl-substituted or C2-20 alkenyl-substituted aromatic group. The aromatic group may be, for example, the phenylene group xe2x80x94(C6H4)xe2x80x94, the biphenylene group xe2x80x94(C6H4)xe2x80x94(C6H4)xe2x80x94, the xe2x80x94(C6H4)xe2x80x94Oxe2x80x94(C6H4)xe2x80x94 group, or the naphthylene group xe2x80x94(C10H6)xe2x80x94. R20 may be one of the same groups as R19 with the further proviso that at least one of R19 and R20 must contain a continuous carbon chain of at least 8 carbons in length, uninterrupted by any heteroatoms.
As stated above, if R19 and R20 are other than hydrogen, the carbon atom attached to the nitrogen atom is not tertiary. Preferably the carbon atom attached to the nitrogen atom is primary, i.e., xe2x80x94CH2xe2x80x94.
It is preferred that R19 is a mono-unsaturated alkenyl group of 12-20 carbons in length and most preferable that R19 is a monounsaturated alkenyl group of 16 to 18 carbons in length. It is most preferable also that R20 is H.
Alternatively, R12 may be a moiety which contains a mineral acid salt or a quaternary ammonium salt of an amine. The formula of R12 may thus be described by the extended formula xe2x80x94R18xe2x80x94NR19R20.R21x wherein xe2x80x94R18xe2x80x94, R19 and R20 are as previously defined and R21 may be a H, or a C1-40 alkyl or C2-40 mono-, di- or tri-unsaturated alkenyl group and X is an anion, preferably Cl or Br, although sulphate can be used.
There is the further proviso that at least one of R19 and R20 must contain a continuous carbon chain of at least 8 carbons in length, uninterrupted by any heteroatom. It is preferred to use an amine salt where R19 is a mono- or di-unsaturated alkenyl group of 12-20 carbons in length and most preferably that R19 is a mono- or di-unsaturated alkenyl group of 16 to 18 carbons in length. It is most preferable also that R20 is H and that R21 is H and X is chlorine. The preferred hydrophobicizing agent of Formula II is N-oleyl-N-(3-trimethoxysilyl)propyl ammonium chloride.
Preferably, the amount of the hydrophobic compound of Formula II to add is generally between 0.5 and 20 percent by weight of the weight of the particles (preferably mineral particles such as silica) in the slurry (dry basis), and is inversely proportional to the particle size of the silica particles. The compound may be added to the slurry in its natural state, either as a liquid or a solid. However, to facilitate dispersion, it is preferred, where possible, to add the compound as a liquid. If the melting point of the compound is below 95 degrees Celsius, it is preferred to add it to the slurry in a molten state at a temperature at least 5 degrees Celsius above the melting point, provided the temperature of the compound in the liquified state does not exceed 100 degrees Celsius and provided that the compound does not decompose under these conditions. If the melting point exceeds 95 degrees Celsius, it is most preferred to use a solvent. Suitable solvents are alcohols containing 1 to 5 carbon atoms and most preferably those containing 1 to 3 carbon atoms, that is to say methanol, ethanol, n-propanol or isopropanol. If the compound of Formula II is an alkoxysilane, most preferably the alkoxy group of the solvent alcohol will be the same as the alkoxy group of the alkoxysilane. For example, if the compound of Formula II is a methoxysilane, the preferred solvent is methanol. The concentration of the compound in the solvent may be from 10 to 90 percent by weight and most preferably between 25 and 75 percent by weight and most preferably 50 percent by weight. Preferably, the solution is prepared and added to the slurry at a temperature between a lower limit of 0 degrees Celsius and an upper limit which is the lower of at least 10 degrees below the boiling point of the solvent and 95 degrees Celsius.
After the addition of the hydrophobic compound of Formula II which is added, the equivalent balance (EB) should be calculated to determine how much, if any, mineral acid or alkali metal hydroxide (or solutions thereof) to add. The equivalent balance (EB) may be determined from the absolute value of the sum of the group values of X, R15, R16 and R17 and the weight added, and the molecular weight of the compound, according to the following scheme: The group contribution of X for either X=Cl or X=Br is xe2x88x921, thus if X is present it is given a value of xe2x88x921. The group contribution of each of R15, R16 and R17 is generally zero for all groups except as follows: if the group is CH3COOxe2x8ax96, Clxe2x8ax96 or Brxe2x8ax96, in which case it is xe2x88x921, or if it is amino, ONa, OK, or OLi in which case it is +1. If the sum of the group contributions for X, R15 , R16 and R17 is zero, no adjustment with mineral acid or alkali metal hydroxide (or solutions thereof is necessary. If the sum of the group values is a positive integer, adjustment with mineral acid is desirable, and if it is negative, adjustment with alkali hydroxide is desirable.
For example, where R15=OC2H5, R16=OCH3 R17=CH3 and X=Cl, the sum xcexa3 of the group values (g.v.) is:
xcexa3=(g.v. OC2H5)+(g.v. OCH3)+(g.v. CH3)+(g.v. Cl)=(0)+(0)+(0)+(xe2x88x921)=xe2x88x921.
The negative sign in front of the sum indicates adjustment with alkali metal hydroxide is required. The number of equivalents of alkali required is given by the equivalent balance (EB) which includes the absolute value of the sum of the group contributions (|xcexa3|) as a scaling factor.   EB  =                    "LeftBracketingBar"        Σ        "RightBracketingBar"            xc3x97      weight      ⁢              xe2x80x83            ⁢      in      ⁢              xe2x80x83            ⁢      grams      ⁢              xe2x80x83            ⁢      of      ⁢              xe2x80x83            ⁢      the      ⁢              xe2x80x83            ⁢      compound      ⁢              xe2x80x83            ⁢      added              molecular      ⁢              xe2x80x83            ⁢      weight      ⁢              xe2x80x83            ⁢      of      ⁢              xe2x80x83            ⁢      the      ⁢              xe2x80x83            ⁢      added      ⁢              xe2x80x83            ⁢              chemical        .            
In continuing the example, if a process according to the present invention were scaled so as to require 3450 grams of a compound of Formula II with a molecular weight of 466 grams and the sum of the group values gave xe2x88x921, EB would be calculated as follows:
EB=|xe2x88x921|xc3x973450/466=7.4 gram-equivalents.
Thus, in this example, 7.4 gram-equivalents of alkali metal hydroxide would be added. Sodium hydroxide is the preferred alkali metal hydroxide. The weight of sodium hydroxide added would be:
Weight=(EB)xc3x97(Equivalent Weight of NaOH)=7.4xc3x9740.0=296 grams.
The preferred technique according to the invention is to dissolve the alkali hydroxide or mineral acid in water so as to obtain a concentration between 5 and 25% by weight and mos t preferably between 5 and 10% by weight prior to adding the solution to the slurry. The temperature of the solution may be from 0 degrees Celsius to 100 degrees Celsius under atmospheric pressure, or if a pressure vessel is used for preparation of the solution, it may be from 0 degrees Celsius to 130 degrees Celsius. It is preferred that the temperature of the solution be within 10 degrees of the solution of the slurry. The dispersion of the solution in the slurry is effected by mixing.
The process described thus far provides an aqueous slurry or dispersion of hydrophobicized silica (i.e., it has not yet been contacted with an elastomer or other substrate to be filled), which can be used as such or can be filtered and dried. In a preferred embodiment, the hydrophobicized silica, in the aqueous dispersion or slurry, is mixed with a hydrocarbon or or other solution of solution SBR (including low vinyl, low styrene solution SBR), solution BR or mixtures thereof to form a rubber masterbatch. It is particularly preferred that the hydrophobicized silica shall have been treated with a coupling agent, for example Si-69, Si-168 or Silquest RC-2, as discussed above. Preferably, the solvent in which the elastomer is dissolved is immiscible with, or mostly immiscible with, water to form a preblend. This elastomer solution may be made by dissolving the solid elastomer in a solvent, or it may be the solution resulting from the polymerisation of monomers in the solvent. Optionally, processing oil and antioxidants may be added to the hydrocarbon solution prior to mixing with the slurry, or they may be added after mixing the slurry and the elastomer solution.
The viscosity of the final elastomer solution, sometimes referred to as an elastomer cement, containing the optional ingredients is preferably such that it closely matches the viscosity of the silica slurry and is generally between 1,000 and 50,000 centipoise. The temperature of the elastomer solution is preferably the same as that of the slurry and the amount of cement that is added is such that the final masterbatch may contain from 5 to 250 parts of silica per hundred parts of elastomer, preferably from 35 to 100 parts of silica per hundred parts of elastomer, most preferably from 60 to 80 parts of silica per hundred parts of elastomer.
The elastomer cement and, optionally, oil and antioxidants, is mixed with the silica slurry until the mixture becomes homogeneous and the milky colour of the silica slurry disappears to form a preblend. A small amount of water may separate at this stage.
If not added previously, or if additional amounts are desired, oil and antioxidants may be added next and the mixing continued further until the oil and antioxidant become incorporated in the continuous phase.
Any water which separates from the preblend may be removed, discarded or recycled for silica slurry make-up by stopping the agitator for a suitable period and allowing the water phase to accumulate in the bottom of the mixing tank from which it may be drained prior to proceeding with the next step. Agitation is preferably restarted after the water layer is removed.
If antioxidants and processing oil were not previously added, or if additional amounts are desired, they may be added at this stage and stirring continued until the preblend is again homogeneous.
The preblend is then added to water heated to a temperature equal to, or preferably higher than the boiling point of the solvent used for the elastomer cement so as to remove the solvent and produce a masterbatch coagulum in the form of a crumb suspended in water. The preferable temperature of the water prior to addition of the preblend is between 50 and 100 degrees Celsius, most preferably between 90 and 95 degrees Celsius, and the preblend is added at a rate so as to maintain a so-fixed or reasonably so-fixed water temperature throughout the coagulation. The agitation is set sufficiently high so as to maintain the crumb in a suspended state within the water but not so high as to cause the crumb to subdivide into particles smaller than approximately 5 millimeters.
The solvent may be recovered from the coagulator by recondensing the vapours. The material containing the suspended crumb is passed through a filter screen sized so as to recover the wet masterbatch. The material passing through the screen may be optionally recycled for further silica slurry make-up.
The wet crumb is dried such as by using forced air or fluidized bed or microwave drying techniques at a temperature between about 75 and about 135 degrees Celsius, preferably between about 85 and about 120 degrees Celsius, most preferably between about 85 and about 105 degrees Celsius, until a suitably dry masterbatch crumb is obtained.
The dried crumb may be further processed according to industry and customer requirements.